Grounding, Bonding, and Electrical Protection
What this domain covers
Grounding, Bonding, and Electrical Protection tests the difference between grounding and bonding and the specific rules for low-voltage and communications systems. Expect Article 250 fundamentals plus 800.100, 820.93, 810.21, and intersystem bonding termination.
Core rules
- Grounding connects an electrical system to the earth; bonding connects metal parts together to create an equipotential plane. Bonding is the safety function; a ground rod alone does not clear a fault.
- The equipment grounding conductor provides the low-impedance fault path back to the source and must be continuous, correctly sized, and not used as a current-carrying neutral.
- Communications systems have their own grounding rules. Under Article 800, the communications grounding conductor is copper, not smaller than 14 AWG, continuous, and connected to the grounding electrode conductor, the grounding electrode, or an intersystem bonding termination. Keep it as short and straight as practicable.
- Coaxial cable shields for CATV and radio distribution must be grounded at the point of entry, generally with a copper conductor not smaller than 14 AWG, in accordance with Article 820. Antenna and lead-in grounding under Article 810 generally uses a 10 AWG copper conductor.
- An intersystem bonding termination is the common point for communications, CATV, and satellite grounding. It must be accessible and connected to the grounding electrode system.
- Surge protective devices, GFCI protection, and AFCI protection are part of the protection picture, but they do not replace bonding. Low-voltage circuits can still create fire and shock hazards through power supplies, PoE, and faulted cables.
Worked example
A coaxial cable from a cable TV provider enters a building and terminates at a splitter. The splitter is not grounded. The installer should fit a listed ground block, run a 14 AWG copper conductor from the block to the intersystem bonding termination or grounding electrode conductor, and keep the run as short and straight as possible. The reasoning is that the shield can carry fault current or lightning-induced surge; grounding at the entry point limits the potential difference between the coaxial shield and the building's grounded metal.
Traps that cost marks
Calling a ground rod a bond; using the neutral as a ground; daisy-chaining communications grounds; grounding a shield at both ends of a data cable and creating a ground loop; using a green conductor for a current-carrying circuit; and assuming low-voltage systems are exempt from Article 250.